This invention relates to extruded polymeric netting and more particularly to such netting in which at least some of the strands in at least one direction in the net, preferably all of the strands, are of an elastomeric polymeric material which may be stretch modified in accordance with this invention.
Extruded polymeric netting has been known and used for some time. U.S. Pat. No. 4,152,479 to Larsen and U.S. Pat. No. 3,252,181 to Hureau describe types of such net. These patents and their entire content are incorporated herein by reference. Extruded netting is netting in which the strands are extruded from a die, the joints therebetween being formed either within the die or immediately outside the lips of the die.
In the netting to which these patents relate, the extruded strands are comprised of orientable polymeric material. Orientation is a stretching process which can be applied to the net in the machine direction (MD) and/or the cross direction (CD) or transverse direction (TD). When oriented in only one direction, the net is said to be uniaxially oriented. When oriented in both directions it is said to be biaxially oriented.
The orientation process is applied to these types of net to significantly increase net size, both in width and length and to orient the molecules of the material in the strands from a random arrangement into a more ordered arrangement. Due to the nature of the polymeric material used heretofore in extruded netting, the net when stretched to a larger size remained essentially at the stretched or enlarged size. That is, such nets do not exhibit any significant recovery. The ordered arrangement obtained is desirable because it increases the strength to weight ratio of the net. Some of the more common materials used in such nets are polypropylene, nylon and linear low density and high density polyethylene.
It has recently become desirable to provide extruded net in which the strands or at least some of the strands in one direction or both directions are of elastomeric material in order to provide net exhibiting significant elasticity for a variety of purposes. One such net is described in co-pending application Ser. No. 08/295,635 entitled BICOMPONENT ELASTOMERIC NETTING which is assigned to the same assignee as is this invention. The content of this application is incorporated herein by reference.
Stretch orientation processing has not been applied to elastomeric net to modify elastic properties prior to this invention. It has not been believed that the orientation process would be useful with respect to extruded elastomeric nets since it does not provide the traditionally expected results and benefits.
In accordance with this invention, it has been discovered that stretching elastomeric strands in extruded netting produces beneficial modification of the elastic properties of the net. The invention most accurately is described herein as "stretch modification". The same equipment as is used for orientation may be used for stretch modification when modified to accommodate the greater stretch involved. Such equipment is described in the aforenoted Larsen patent. Stretch modification may take place at room temperature (RT) or at elevated temperatures, similar to the known orientation process.